Control process and apparatus for membrane separation systems

Abstract

A process and an apparatus are disclosed for controlling the concentration of a component in an effluent stream from a permeable membrane gas separation system. A gaseous feed stream is passed to the membrane system at a substantially constant flow and elevated pressure. Control is achieved by sensing a characteristic of an effluent stream that is indicative of the concentration of the component, i.e., permeate or non-permeate stream, and performing a pressure adjustment on the permeate stream or non-permeate stream, to vary the concentration of the component in the effluent stream as necessary to obtain a predetermined concentration of the component in the effluent stream. A product stream having a relatively constant pressure and purity can be obtained by sensing a characteristic of a desired effluent stream, e.g., permeate, and performing a pressure adjustment on the other effluent stream, e.g., non-permeate.

What is claimed is: 
     
       1. In a permeable membrane gas separation process which comprises: (a) passing a gaseous feed stream comprising a component to a permeable membrane gas separation system at a substantially constant flow rate and elevated feed pressure, said feed pressure being equal to or higher than the pressure required to operate the permeable membrane gas separation system and said feed stream being subject to fluctuations in composition; and   (b) recovering from said permeable membrane gas separation system, an effluent stream comprising a permeate stream or a non-permeate stream; the improvement which comprises controlling the concentration of said component in said effluent stream by; 1) sensing a change in a characteristic of said effluent stream that is indicative of a change in the concentration of said component in said feed stream of from about 1 to 30%; and   2) without substantially altering the feed pressure or flow rate, performing a pressure adjustment on said permeate stream or said non-permeate stream in response to said sensed characteristic to alter the concentration of said component in said effluent stream as necessary to obtain a predetermined concentration of said component in said effluent stream.     
     
     
       2. A process according to claim 1 wherein said sensed characteristic is the concentration of said component in said effluent stream. 
     
     
       3. A process according to claim 1 wherein said effluent stream comprises said permeate stream. 
     
     
       4. A process according to claim 3 wherein said pressure adjustment is performed on said non-permeate stream. 
     
     
       5. A process according to claim 1 wherein said effluent stream comprises said non-permeate stream. 
     
     
       6. A process according to claim 5 wherein said pressure adjustment is performed on said permeate stream. 
     
     
       7. A process according to claim 1 including the further steps of: sensing the concentration of said component in said effluent stream; comparing the sensed concentration to a reference value; and establishing a target value of said effluent stream in response to the comparison of the sensed concentration and the reference value. 
     
     
       8. A process for controlling the concentration of a component in a permeate effluent stream from a permeable membrane gas separation system, which comprises: (a) passing a gaseous feed stream comprising said component and at least one other component to the permeable membrane gas separation system at a substantially constant flow rate and feed pressure of at least about 100 psia, said feed pressure being equal to or greater than the pressure required to operate the permeable membrane gas separation system and said feed stream being subject to fluctuations in composition;   (b) recovering a non-permeate effluent stream enriched in the at least one other component relative to said feed stream;   (c) recovering a permeate effluent stream enriched in said component relative to said feed stream;   (d) sensing a change in the concentration of said component in said permeate effluent stream that is indicative of a change in the concentration of said component in said feed stream of from about 1 to 30%; and   (e) without substantially altering the feed pressure or flow rate, performing a pressure adjustment on said nonpermeate eflfuent stream in response to said sensed concentration to alter the concentration of said component in said permeate effluent stream as necessary to obtain a predetermined concentration of said component in said permeate stream without substantially altering the pressure of said permeate stream.   
     
     
       9. A process according to claim 8 wherein said feed pressure is in the range of from about 500 to about 2000 psia. 
     
     
       10. A process according to claim 8 wherein said component is hydrogen. 
     
     
       11. A process according to claim 10 wherein the at least one other component comprises hydrocarbons in the C1 to C5 carbon range. 
     
     
       12. A process for controlling the concentration of a component in a non-permeate effluent stream from a permeable membrane gas separation system, which comprises: (a) passing a gaseous feed stream comprising said component and at least one other component to the permeable membrane gas separation system at a substantially constant flow rate and feed pressure of at least about 100 psia, said feed pressure being equal to or greater than the pressure required to operate the permeable membrane gas separation system and said feed stream being subject to fluctuations in composition;   (b) recovering a non-permeate effluent stream enriched in said component relative to said feed stream;   (c) recovering a permeate effluent stream enriched in the at least one other component relative to said feed stream;   (d) sensing a change in the concentration of said component in said non-permeate effluent stream that is indicative of a change in the concentration of said component in said feed stream of from about 1 to 30%; and   (e) without substantially altering the feed pressure or flow rate, performing a pressure adjustment on said permeate effuent stream in response to said sensed concentration to alter the concentration of said component in said non-permeate effluent stream as necessary to obtain a predetermined concentration of said component in said non-permeate stream without substantially altering the pressure of said non-permeate stream.   
     
     
       13. A process according to claim 12 wherein said component comprises natural gas hydrocarbons. 
     
     
       14. A process according to claim 13 wherein the at least one other component is carbon dioxide. 
     
     
       15. A process according to claim 12 wherein said component comprises a mixture of hydrogen and carbon monoxide in a molar ratio of from about 1 to 4 moles of hydrogen per mole of carbon monoxide. 
     
     
       16. A process according to claim 15 wherein the at least one other component is carbon dioxide.